the problem with a single led is not so much that freetrack can't deduce information from it, but rather that you can't have multiple degrees of freedom. I believe freetrack is preset to interpret single led displacement as rotations, but it would not be difficult to change that into translations.
If you have two camera's you'll be able to accurately deduce where the led is in 3d space, but you will still not be able to deduce what type of movement, translation or rotation, got it to that position, hence you will not be able to have all 6 degrees supported.
Furthermore, which I also find strange, Freetrack doesn't care at all where your head is in space, all it does is compare one image with another, regardless of how it was obtained. As illustration: I have my cam looking through a mirror, and reversed the output in FT, which works fine.
EDIT: by the way, this isn't tooo nerdy is it?